Who Was That Lady?by Simon Pegg and Edgar Wright (Based On The Play "Who Was That Lady I Saw You With?" by Norman Krasna)

When a chemistry professor's wife walks in on him just as a grateful female student gives him an innocent kiss, it causes strains in the marriage. When she finds the truth difficult to believe (in part because he had secretly been tutoring the young woman), the professor turns to a writer friend for some help, and HE comes up with the idea of telling his wife that he's working undercover for the FBI and that the student was actually a contact in a case involving a terrorist ring. To his total amazement, the wife believes it, but very soon, actual FBI agents, and actual terrorists become involved, and things get a bit desperate . . .